Apparatus for transmitting and receiving data to provide high-speed data communication and method thereof

ABSTRACT

In the present invention, data generated from a source unit are distributed to at least one bandwidth; the data distributed to the respective bandwidths are encoded in order to perform an error correction; the encoded data are distributed to at least one antenna; a subcarrier is allocated to the data distributed to the respective antennas, and an inverse Fourier transform is performed; a short preamble and a first long preamble corresponding to the subcarrier are generated; a signal symbol is generated according to a data transmit mode; and a frame is generated by adding a second long preamble between the signal symbol and a data field for the purpose of estimating a channel of a subcarrier which is not used.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/401,293, filed Mar. 10, 2009, which is a continuation of Ser. No.11/767,797 filed Jun. 25, 2007, and claims priority to InternationalApplication PCT/KR2005/000393 filed Feb. 11, 2005 and Korean ApplicationNo. 10-2004-0111065, filed on Dec. 23, 2004, the disclosures of allwhich are hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to an apparatus for transmitting andreceiving data in radio data communication. More specifically, thepresent invention relates to an apparatus compatible with a conventionalwireless local area network communication system, for transmitting andreceiving data in high-speed and a method thereof. In addition, thepresent invention relates to a wireless communication system forincreasing data rates from 54 Mbps which has been a maximum data rate inthe conventional wireless local area network communication system, tohundreds of Mbps.

2. Description of the Related Art

In the conventional IEEE 802.11a wireless local area network (LAN)system using an orthogonal frequency division multiplexing method, a Hzbandwidth is divided into 64 subcarriers, and 52 subcarriers of the 64subcarriers are used to transmit data and pilot symbols. That is, thedata are transmitted at a maximum speed of 54 Mbps by using a singleantenna and the 20 MHz bandwidth.

The present invention provides an apparatus for transmitting andreceiving data while being compatible with the conventional IEEE 802.11aorthogonal frequency division multiplexing (OFDM) method. The apparatususes multiple antennas and a plurality of 20 MHz bandwidths to achieve ahigh data rate.

In response to the demand for high-speed multimedia data transmission,various practical applications requesting more than 100 Mbps throughputhave been being developed. However, even the wireless LAN system havingthe greatest throughput of the current wireless communication systemsdoes not offer over 25 Mbps of throughputs. Therefore the presentinvention suggests a system offering a data rate which is four times asfast as the conventional IEEE 802.11a system, or more.

In detail, the present invention suggests a configuration in which anumber of antennas and bandwidths are systematically controlled and amaximum data rate is controlled according to characteristics of asystem. The present invention also suggests a method for providingcompatibility with the conventional system.

FIG. 1 shows a block diagram for representing a system for transmittingand receiving data in the conventional wireless LAN.

In the conventional IEEE 802.11a system shown in FIG. 1, 20 MHzbandwidth is divided into 64 subcarriers. Among the 84 subcarriers, 48subcarriers are used for data transmission 4 subcarriers are used forpilot symbol transmission, and a DC subcarrier and the other 11subcarriers are not used.

A convolutional code having ½, ⅔, and ¾ code rates, binary phase shiftkeying (BPSK) modulation, quaternary phase shift keying (QPSK)modulation, 16 quadrature amplitude modulation (QAM) modulation, and 64quadrature amplitude modulation (QAM) are used to transmit the data.

In the system shown in FIG. 1, when a source unit 101 generates binarydata, the binary data are provided to a scrambler 102 for randomizing apermutation of the binary data.

A convolution encoder 103 performs channel encoding according to a coderate and a modulation determined by a desired data rate, and a mapper105 performs modulation to map the previous data permutation on acomplex symbol permutation.

An interleaver 104 provided between the convolution encoder 103 and themapper 105 interleaves the data permutation according to a predeterminedrule. The mapper 105 establishes the complex number permutation to be agroup of 48, and a subcarrier allocator 107 forms 48 data components and4 pilot components from pilot unit 106.

A 64 inverse fast Fourier transform (64-IFFT) unit 108 performs aninverse fast Fourier transform on the 48 data and 4 pilot components toform an OFDM symbol.

A cyclic prefix adder 109 adds a cyclic prefix which is a guard intervalto the OFDM symbol.

A radio frequency (RF) transmit unit 110 transmits a transmission frameformed by the above configuration on a carrier frequency. An RF receiveunit 112 receives the transmission signal (the transmission frametransmitted on the carrier frequency) through a radio channel 111. Theradio channel 111 includes a multi-path fading channel and Gaussiannoise added from a receive terminal.

The RF receive unit 112 of the receive terminal receives the distortedsignal passing through the radio channel 111, and down-converts thesignal transmitted on the carrier frequency to a base band signal in anopposite manner executed by the RF transmit unit 110 of the transmitterminal.

A cyclic prefix eliminator 113 eliminates the cyclic prefix added in atransmitter. A 64 fast Fourier transform (64-FFT) unit 114 converts areceived OFDM symbol into a signal of a frequency domain by performingan FFT operation.

A subcarrier extractor 115 transmits the 48 complex symbolscorresponding to the data subcarrier among 64 outputs to an equalizingand tracking unit 117, and transmits the 4 subcarriers corresponding tothe pilot to an equalizing and tracking parameter estimator 116.

The equalizing and tracking parameter estimator 116 estimates a phasechange caused by frequency and time errors by using the known symbols,and transmits an estimation result to the equalizing and tracking unit117.

The equalizing and tracking unit 117 uses the above estimation result toperform a tracking operation. The equalizing and tracking unit 117 alsoperforms a frequency domain channel equalization operation forequalizing channel distortion in the frequency domain in addition to thetracking process.

A demapper 118 performs a hard decision operation for converting theoutput complex number after the channel equalizing and trackingoperation into the binary data, or performs a soft decision forconverting the output complex number into a real number. A deinterleaver119 deinterleaves the data in an inverse process of the interleaver 104,and a Viterbi decoder 120 performs decoding of the convolution code tocorrect errors and restore the transmitted data.

A descrambler 121 randomizes the data transmitted from the source unitin a like manner of the scrambler 102 and transmits the received data toa sink unit 122.

The conventional wireless LAN system shown in FIG. 1 has limits of datarate and throughput, and therefore the system is difficult to apply to aservice requiring a high data rate such as a high quality moving pictureservice.

Systems using multiple bandwidths and antennas to provide a high speeddata rate have previously not been compatible with the conventionaltransmitting and receiving system.

Accordingly, the present invention provides an apparatus fortransmitting and receiving for providing compatibility with theconventional wireless communication system, and the high speed data rateand a method thereof.

SUMMARY OF THE INVENTION Technical Problem

The present invention provides a data transmitting and receiving deviceto provide a high data rate and compatibility with the conventionalwireless communication system, and a method thereof.

Technical Solution

The present invention provides a data transmitting and receiving deviceto provide a high data rate and compatibility with the conventionalwireless communication system, and a method thereof.

The present invention discloses a data transmitting device including abandwidth distributor, an encoder, a mapper, an antenna distributor, asubcarrier allocator, an inverse Fourier transform unit, a preamblegenerator, and a frame generator.

The bandwidth distributor distributes data generated in a source unit toat least one bandwidth. The encoder performs encoding of the distributeddata in order to perform error correction of the data. The mapperperforms mapping of the encoded data into a complex number symbol. Theantenna distributor distributes the complex number symbol to at leastone antenna. The subcarrier allocator allocates a subcarrier fororthogonal frequency division multiplexing to the distributed complexnumber symbol. The inverse Fourier transform unit performs an inverseFourier transform of the OFDM signal to which the subcarrier isallocated. The preamble generator generates a short preamble, a firstlong preamble, and a second long preamble of the subcarrier. The framegenerator generates frames in an order of the short preamble, the firstlong preamble, a signal symbol, the second long preamble, and a datafield. At this time, one of the first long preambles of a second antennamay be used for the second long preamble in order to perform a channelestimation of a subcarrier which is not used by a first antenna when twoor more antennas are used.

The signal symbol generated by the frame generator comprises a transmitmode identifier for determining whether a transmit mode is a singleantenna transmit mode or a multiple-input/multiple-output (MIMO) mode.

The transmit mode Identifier uses an R4 bit of the signal symbols in aframe of IEEE 802.11a.

A reserved bit of the signal symbol is used as a bit for determiningwhether the transmit mode uses a spatial division multiplexing (SDM)method or a space-time block code (STBC) method.

The data transmitting device according to the exemplary embodiment ofthe present invention further includes a scrambler, an interleaver, acyclic prefix adder, and an RF transmit unit.

The scrambler is coupled between the bandwidth distributor and theencoder and performs a scrambling operation. The interleaver is coupledbetween the encoder and the mapper and performs an interleavingoperation. The cyclic prefix adder adds a cyclic prefix to aninverse-Fourier-transformed orthogonal frequency division multiplexing(OFDM) signal. The RF transmit unit transmits the frame through a radiochannel. The antenna distributor distributes the mapped symbols toantennas or encodes STBC.

The present invention discloses a data receiving device including an RFreceiving unit, a channel mixer, an initial synchronizer, a Fouriertransforming unit a signal symbol demodulator, a channel estimator, anda detector.

The RF receiving unit receives a frame through a radio channel. Thechannel mixer performs a channel mixing operation in order to extract a20 MHz short preamble and a 20 MHz first long preamble from the receivedframe. The initial synchronizer performs an initial synchronizingoperation by using the extracted short preamble and first long preamble.The Fourier transforming unit performs a Fourier transforming operationof the frame. The signal symbol demodulator demodulates a signal symboland demodulates information on a transmit mode. The channel estimatorperforms a first channel estimation by using the first long preamble,and performs a second channel estimation by using a second long preambletransmitting after the signal symbol when the information on thetransmit mode is a MIMO-OFDM transmit mode The detector detects acomplex number symbol corresponding to the data with reference to theestimated channel and demodulated signal symbol. We detect a transmitmode identifier established in the signal symbol, and determine whetherthe transmit mode is a single antenna transmit mode or a MIMO-OFDMtransmit mode.

The channel estimator uses the second long preamble to perform thesecond channel estimation of a subcarrier which is not used by a firstantenna.

The data receiving device further includes a cyclic prefix eliminator, asubcarrier extractor, a demapper, a deinterleaver, and an errorcorrection decoder.

The cyclic prefix eliminator eliminates a cyclic prefix of the signalreceived from the RF receiving unit. The subcarrier extractor extractssubcarriers from the Fourier-transformed signal and combines thesubcarriers. The demapper performs demapping of the signal demodulatedto the complex number signal into a binary data signal. Thedeinterleaver performs deinterleaving of the demapped signal. The errorcorrection decoder performs an error correction decoding operation onthe deinterleaved signal. The detector is a SDM detector or a STBCdecoder.

Advantageous Effect

According to the present invention, an increased data rata is providedby using multiple bandwidths and antennas in a wireless communicationsystem.

Because of compatibility with the conventional system, the increaseddata rate is provided without modifying the existing device and design.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram for representing a conventionaltransmitting and receiving system in the wireless LAN.

FIG. 2 shows a block diagram for representing a configuration of atransmitter according to an exemplary embodiment of the presentinvention.

FIG. 3 shows a block diagram for representing a configuration of areceiver according to the exemplary embodiment of the present invention.

FIG. 4 shows an OFDM subcarrier allocation method supporting a singlebandwidth and an OFDM subcarrier allocation method for supportingmultiple bandwidths.

FIG. 5 shows a diagram for representing the IEEE 802.11a frameconfiguration.

FIG. 6 shows a diagram for representing the frame configurationaccording to an exemplary embodiment of the present invention.

FIG. 7 shows a block diagram for representing a configuration forinitial synchronization of the receiver according to an exemplaryembodiment of the present invention.

FIG. 8 shows a flow chart for representing a method for transmitting thedata according to an exemplary embodiment of the present invention.

FIG. 9 shows a flow chart for representing a method for receiving thedata according to an exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following detailed description, only the preferred embodiment ofthe invention has been shown and described, simply by way ofillustration of the best mode contemplated by the inversions) ofcarrying out the invention. As will be realized, the invention iscapable of modification in various obvious respects, all withoutdeparting from the invention. Accordingly the drawings and descriptionare to be regarded as illustrative in nature, and not restrictive. Toclarify the present invention, parts which are not described in thespecification are omitted, and parts for which same descriptions areprovided have the same reference numerals.

While this invention is described in connection with what is presentlyconsidered to be the most practical and preferred embodiment, it is tobe understood that the invention is not limited to the disclosedembodiment, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

FIG. 2 shows a block diagram for representing a configuration of atransmitter according to an exemplary embodiment of the presentinvention.

The transmitter includes a source unit 201, a bandwidth distributor 202,scrambler/convolution encoders 2031 to 203L, an interleaver 204, amapper 205, a pilot unit 206, an antenna distributor 207, subcarrierallocators 2081 to 208M, IFFT units 2091 to 209M, cyclic prefix adders2101 to 210M, preamble generators 2301 to 230M, frame generators 2311 to231M, and RF transmit units 2111 to 211M.

When binary data generated in the source unit 201 are transmitted to thebandwidth distributor 202, the bandwidth distributor 202 distributes thebinary data to L bandwidths according to a number (L) of 20 MHzbandwidths to be used in the band distributor 202.

The scrambler/convolution encoders 2031 to 203L perform scrambling andconvolutional code encoding operations for the respective bandwidths.

The interleaver 204 receives the convolutionally encoded data. At thistime, two types of interleaves 204 are available. One interleaverperforms interleaving of each OFDM symbol of the respective bandwidthsin a like manner of the scrambler/convolution encoders 2031 to 203L, andthe other interleaver performs interleaving of the L number of OFDMsymbols in every bandwidth. The former interleaver is simple and easy tounderstand, and the latter interleaver is complex to be realized and itis expected to obtain performance gain due to diversity gain.

The mapper 205 converts the binary data into complex symbols. Theconverted complex symbols are distributed to M number of transmitantennas by the antenna distributor 207. The subcarrier allocators 2081to 208M use pilot symbols from the pilot unit 208 and the distributeddata complex symbols in order to allocate subcarriers for OFDMmodulation. Allocation of the subcarriers will be described later.

Frequency domain OFDM symbols corresponding to the allocated M number ofthe transmit antennas are inverse-Fourier-transformed into time domainOFDM symbols by the (L*64)-IFFT units 2091 to 209M. The cyclic prefixadders 2101 to 210M add cyclic prefixes corresponding to the OFDMsymbols of each path.

The frame generators 2311 to 231M generate proper frames for a systemshown in FIG. 2. Similar to the conventional IEEE 802.11a frameconfiguration a frame configuration according to an exemplary embodimentof the present invention includes a short preamble, a first longpreamble, a signal symbol, and data. In addition, the frameconfiguration includes a second long preamble in the preamble generators2301 to 230M. The second long preamble is a long preamble having beenused in another antenna, and multiple-input/multiple-output (MIMO)channel estimation on the subcarriers is performed by the second longpreamble.

The preamble generators 2301 to 230M generate the short preamble, thefirst long preamble, and the second long preamble, and provide the sameto the frame generators 2311 to 231M.

The frame used in the exemplary embodiment of the present invention willbe described later.

FIG. 3 shows a block diagram for representing a receiver according tothe exemplary embodiment of the present invention.

The receiver shown in FIG. 3 performs an inverse operation on the signaltransmitted from the transmitter shown in FIG. 2.

The signal transmitted through the channel 212 from the transmitter isreceived by N number of receive antennas in N number of RF receive units2131 to 213N. The received signal is restored to a transmit signal whilepassing through cyclic prefix eliminators 2141 to 214N, (L*64) FFT units2151 to 215N, subcarrier extractors 2161 to 216N, a channel and trackingparameter estimation unit 217, an MIMO detector 218, a demapper 219, adeinterleaver 220, descrambler/Viterbi decoders 2211 to 221L, and abandwidth combining unit 222, and data are transmitted to a sink unit223.

A demodulation process of the receiver shown in FIG. 3 is similar tothat of the receiver shown in FIG. 1. However, the channel estimationunit 217 in the receiver shown in FIG. 3 estimates the MIMO channel,which is different from the system shown in FIG. 1. In addition, theequalizing unit 117 shown in FIG. 1 is substituted to the MIMO detector218 in the system shown in FIG. 3. A configuration of the deinterleaverhas to be changed according to a varied configuration of theinterleaver.

The bandwidth combining unit 222 added in the system shown in FIG. 3performs an inverse operation of the bandwidth distributor 202 of thetransmitter shown in FIG. 2.

While the (L*64) IF FT and (L*64) FFT are used in FIG. 2 and FIG. 3, Lnumber of 64 FFTs and 64 IFFTs may be used, and one (L*64) IFFT and one(L*64) FFT may be also used. These modifications are apparent to thoseskilled in the art.

FIG. 3 shows a receiving and demodulating configuration incorrespondence to the MIMO transmitter shown in FIG. 2, and aconfiguration of the receiver for performing initial synchronization andchannel estimation will be described later.

In FIG. 2, a spatial division multiplexing (SDM) method for increasingthe data rate by using the multiple transmit/receive antennas has beendescribed.

The SDM method, one of the MIMO methods, increases the data rate bytransmitting independent data via the respective transmit antennas.

When a system is designed for the purpose of broadening a service areaand increasing a signal to noise ratio (SNR) rather than for increasingthe data rate, a space-time block code (STBC) for achieving thediversity gain may be applied to the exemplary embodiment of the presentinvention.

When the STBC is applied in the exemplary embodiment of the presentinvention, the antenna distributor 207 is substituted for an STBCencoder, and the MIMO detector 218 is substituted for an STBC decoder.

For convenience of description, a system including two transmit antennasand two bandwidths will be exemplified to describe the frameconfiguration of the exemplary embodiment of the present invention. Thatis, L is 2 and M is 2 in the system shown in FIG. 2. The conventionalframe configuration and OFDM symbol configuration are used in theexemplary embodiment of the present invention for the purpose ofproviding compatibility with the existing IEEE 802.11a system.

As to the OFDM symbol configuration, a 40 MHz bandwidth is divided into128 subcarriers which are generated by combining two 20 MHz bandwidthseach of which is divided into 64 subcarriers in the prior art in theexemplary embodiment of the present invention. Accordingly, 128-IFFT isused to perform the OFDM modulation in 20 MHZ end 40 MHz bandwidths.

FIG. 4 shows an OFDM subcarrier allocation method supporting a singlebandwidth and an OFDM subcarrier allocation method for supportingmultiplex bandwidths.

A subcarrier allocation configuration (a) is formed when a signal istransmitted by a single antenna and a single bandwidth in theconventional IEEE 802.11a. The configuration (b) according to theexemplary embodiment of the present invention corresponds to that of theconventional IEEE 802.11a when a signal fills a desired bandwidth, 0fills other bandwidths, and the signal is transmitted through the singleantenna.

That is, the data and pilot are allocated in 52 subcarriers between 0and 63, and 0's are filled between −64 and −1 when one side bandwidthhaving a lower frequency is used in a signal configuration (b) using thetwo bandwidths of the subcarrier allocation configuration shown in FIG.4. Accordingly, the system according to the exemplary embodiment of thepresent invention is compatible with the conventional IEEE 802.11asystem because the conventional frame configuration is transmitted inthe new system.

The frame configuration according to the exemplary embodiment of thepresent invention will be described.

FIG. 5 shows a diagram for representing the IEEE 802.11a frameconfiguration.

The IEEE 802.11a frame configuration shown in FIG. 5 includes shortpreambles t1 to t10, long preambles T1 and T2, guard intervals G1 andG2, a signal symbol SIGNAL, and data. The short preamble and the longpreamble are symbols for synchronization and channel estimation in acase of demodulation. The signal symbol includes information on datarate, length, and parity.

The short preamble is a symbol generated by Fourier-transforming an OFDMfrequency domain signal as given in Math Formula 1, and the longpreamble is a symbol generated by Fourier-transforming an OFDM frequencydomain signal as given in Math Formula 2.

S _(−26,26)=√{square root over((13/6))}·{0,0,1+j,0,0,0,−1−j,0,0,0,1+j,0,0,0,−1−j,0,0,0,−1−j,0,0,0,1+j,0,0,0,0,0,0,0,−1−j,0,0,0,−1−j,0,0,0,1+j,0,0,0,1+j,0,0,0,1+j,0,0,0,1+j,0,0}  [MathFormula 1]

L_(−26,26)={1,1,−1,−1,1,1,−1,1,−1,1,1,1,1,1,1,−1,−1,1,1,−1,1,−1,1,1,1,1,0,1,−1,−1,1,1,−1,1,−1,1,−1,−1,−1,−1,−1,1,1,−1,−1,1,−1,1,−1,1,1,1,1}  [MathFormula 2]

The signal symbol includes information on length of data sections (0 to4,095 bytes), code rates (½, ⅔, and ¾), and mapping methods (BPSK, QPSK,16-QAM, and 64-QAM).

For the purpose of providing compatibility with the IEEE 802.11a, frameconfiguration shown in FIG. 5 is slightly modified for thecharacteristics of the multiple antennas when signals are transmittedaccording to the conventional OFDM mode (IEEE 802.11a) in the exemplaryembodiment of the present invention.

When two transmit antennas are used, 52 subcarriers of preambles areequally divided by 26 subcarriers to be transmitted. A second longpreamble is further provided after the signal symbol in order toestimate the channel of the subcarrier which is not used in the firstlong preamble.

The MIMO channel estimation of the subcarriers is performed bytransmitting the first long preamble used as the second long preamble byanother antenna. Accordingly, the length of the long preamble isincreased by the number of the transmit antennas.

A frequency domain signal of the short preamble to be transmitted by thetwo antennas is given by Math FIG. 3. S(0)-26,26 is transmitted by theantenna 0, and S(1)-26,26 is transmitted by the antenna 1.

A frequency domain signal of the first long preamble provided before thesignal symbol is given by Math Formula 4, L(0)-26,26 is transmitted bythe antenna 0, and L(1)-26,26 is transmitted by the antenna 1.

S _(−26,26) ⁽⁰⁾=√{square root over((26/6))}·{0,0,1+j,0,0,0,0,0,0,0,1+j,0,0,0,0,0,0,0,−1−j,0,0,0,0,0,0,0,0,0,0,0,−1−j,0,0,0,0,0,0,0,1+j,0,0,0,0,0,0,0,1+j,0,0,0,0,0,0}

S _(−26,26) ⁽¹⁾=√{square root over((26/6))}·{0,0,0,0,0,0,−1−j,0,0,0,0,0,0,0,−1−j,0,0,0,0,0,0,0,1+j,0,0,0,0,0,0,0,0,0,0,0,−1−j,0,0,0,0,0,0,0,1+j,0,0,0,0,0,0,0,1+j,0,0}  [MathFormula 3]

L _(−26,26) ⁽⁰⁾=√{square root over(2)}·{1,0,−1,0,1,0,−1,0,−1,0,1,0,1,0,1,0,−1,0,1,0,1,0,1,0,1,0,0,0,−1,0,1,0,−1,0,−1,0,−1,0,−1,0,−1,0,1,0,−1,0,−1,0,−1,0,1,0,1}

L _(−26,26) ⁽¹⁾=√{square root over(2)}·{0,1,0,−1,0,1,0,1,0,1,0,1,0,1,0,−1,0,1,0,−1,0,−1,0,1,0,1,0,1,0,−1,0,1,0,1,0,1,0,−1,0,−1,0,1,0,−1,0,1,0,1,0,1,0,1,0}  [Math Formula4]

In a case of the second long preamble following the signal symbol, alocation of the first long preamble is changed so that L(1)-26,26 istransmitted by the antenna 0 and L(0)-26,26 is transmitted by theantenna 1.

FIG. 6 shows a diagram for representing the frame configurationaccording to an exemplary embodiment of the present invention.

As shown in FIG. 6, the frame transmitted by the first antenna (antenna0) uses the even subcarriers to transmit the frame, and the frame isformed by using the first long preamble of the odd subcarriers as thesecond long preamble.

The configuration of the preamble and the signal symbol are repeatedlyconnected to support multiple bandwidths. For example, the shortpreamble and long preamble for the conventional mode (dual band IEEE802.11a) using two bandwidths are represented by Math FIG. 5 and MathFormula 6 when the two bandwidths are used.

S _(−58,58)=√{square root over((13/6))}·{0,0,1+j,0,0,0,−1−j,0,0,0,1+j,0,0,0,−1−j,0,0,0,−1−j,0,0,0,1+j,0,0,0,0,0,0,0,−1−j,0,0,0,−1−j,0,0,0,1+j,0,0,0,1+j,0,0,0,1+j,0,0,0,1+j,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1+j,0,0,0,−1−j,0,0,0,1+j,0,0,0,−1−j,0,0,0,−1−j,0,0,0,1+j,0,0,0,0,0,0,0,−1−j,0,0,0,−1−j,0,0,0,1+j,0,0,0,1+j,0,0,0,1+j,0,0,0,1+j,0,0}  [MathFormula 5]

L_(−58,58)={1,1,−1,−1,1,1,−1,1,−1,1,1,1,1,1,1,−1,−1,1,1,−1,1,−1,1,1,1,1,0,1,−1,−1,1,1,−1,1,−1,1,−1,−1,−1,−1,−1,1,1,−1,−1,1,−1,1,−1,1,1,1,1,0,0,0,0,0,0,0,0,0,0,0,1,1,−1,−1,1,1,−1,1,−1,1,1,1,1,1,1,−1,−1,1,1,−1,1,−1,1,1,1,1,0,1,−1,−1,1,1,−1,1,−1,1,−1,−1,−1,−1,−1,1,1,−1,−1,1,−1,1,−1,1,1,1,1}  [MathFormula 6]

When the two bandwidths and two antennas are used, the short preambleand the long preamble transmitted by the respective antennas are givenby Math Formula 7 and Math Formula 8.

S _(−58,58) ⁽⁰⁾=√{square root over((26/6))}·{0,0,1+j,0,0,0,0,0,0,0,1+j,0,0,0,0,0,0,0,−1−j,0,0,0,0,0,0,0,0,0,0,0,−1−j,0,0,0,0,0,0,0,1+j,0,0,0,0,0,0,0,1+j,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,+j,0,0,0,0,0,0,0,1+j,0,0,0,0,0,0,0,−1−j,0,0,0,0,0,0,0,0,0,0,0,−1−j,0,0,0,0,0,0,0,1+j,0,0,0,0,0,0,0,1+j,0,0,0,0,0,0}

S _(−58,58) ⁽¹⁾=√{square root over((26/6))}·{0,0,0,0,0,0,−1−j,0,0,0,0,0,0,0,−1−j,0,0,0,0,0,0,0,1+j,0,0,0,0,0,0,0,0,0,0,0,−1−j,0,0,0,0,0,0,0,1+j,0,0,0,0,0,0,0,1+j,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,−1−j,0,0,0,0,0,0,0,−1−j,0,0,0,0,0,0,0,1+j,0,0,0,0,0,0,0,0,0,0,0,−1−j,0,0,0,0,0,0,0,1+j,0,0,0,0,0,0,0,1+j,0,0}  [MathFormula 7]

L _(−58,58) ⁽⁰⁾=√{square root over(2)}·{1,0,−1,0,1,0,−1,0,−1,0,1,0,1,0,1,0,−1,0,1,0,1,0,1,0,1,0,0,0,−1,0,1,0,−1,0,−1,0,−1,0,−1,0,−1,0,1,0,−1,0,−1,0,−1,0,1,0,1,0,0,0,0,0,0,0,0,0,0,0,1,0,−1,0,1,0,−1,0,−1,0,1,0,1,0,1,0,−1,0,1,0,1,0,1,0,1,0,0,0,−1,0,1,0,−1,0,−1,0,−1,0,−1,0,−1,0,1,0,−1,0,−1,0,−1,0,1,0,1}

L _(−58,58) ⁽¹⁾=√{square root over(2)}·{0,1,0,−1−1,0,1,0,1,0,1,0,1,0,1,0,−1,0,1,0,−1,0,−1,0,1,0,1,0,1,0,−1,0,1,0,1,0,1,0,−1,0,−1,0,1,0,−1,0,1,0,1,0,1,0,1,0,0,0,0,0,0,0,0,0,0,0,0,1,0,1,−1,0,1,0,1,0,1,0,1,0,1,0,−1,0,1,0,−1,0,−1,0,1,0,1,0,1,0,−1,0,1,0,1,0,1,0,−1,0,−1,0,1,0,−1,0,1,0,1,0,1,0,1,0}  [Math Formula8]

As described above, S(0)-58,58 is transmitted by the antenna 0 andS(1)-58,58 is transmitted by the antenna 1 L(0)-58,58 is transmitted bythe antenna 0, and L(1)-58,58 is transmitted by the antenna 1. However,the second long preamble following the signal symbol is transmitted inan inverse order.

According to the above-described configuration, the receive terminalperforms the channel estimation of the subcarriers by further performingthe channel estimation using the second long preamble withoutdetermining which antenna transmits the signal in the system using themultiple bandwidths and the multiple antennas.

Accordingly, the long preamble is generated in the like manner ofgenerating the long preamble by the preamble generators 2301 to 230Mshown in FIG. 2, and the preamble generators 2301 to 230M additionallyinserts the second long preamble after the signal symbol to generate theframe.

The frame generator modifies the signal symbol in order to providecompatibility with the conventional system.

A bit which has not been used as a reserved bit in the conventionalsymbol configuration is redefined as an antenna bit A and the bit isused for discerning between the SDM and the STBC.

An R4 bit of four RATE bits is used for distinguishing between theconventional IEEE 802.11a mode and the multiple antenna OFDM mode.Accordingly, the frame generator allocates the RATE bits R1 to R4 andthe antenna bit A as shown in Table 1.

TABLE 1 RATE, ANTENNA bit Data Mapping Code Transmit allocation (R1-R4,A) rate method rate mode 1101X 6 BPSK 1/2 IEEE802.11a 1111X 9 BPSK 3/4IEEE802.11a 0101X 12 QPSK 1/2 IEEE802.11a 0111X 18 QPSK 3/4 IEEE802.11a1001X 24 16QAM 1/2 IEEE802.11a 1011X 36 16QAM 3/4 IEEE802.11a 0001X 4864QAM 2/3 IEEE802.11a 0011X 54 64QAM 3/4 IEEE802.11a 11000 6 BPSK 1/2STBC-OFDM 11100 9 BPSK 3/4 STBC-OFDM 01000 12 QPSK 1/2 STBC-OFDM 0110018 QPSK 3/4 STBC-OFDM 10000 24 16QAM 1/2 STBC-OFDM 10100 36 16QAM 3/4STBC-OFDM 00000 48 64QAM 2/3 STBC-OFDM 00100 54 64QAM 3/4 STBC-OFDM11001 12 BPSK 1/2 SDM -OFDM 11101 18 BPSK 3/4 SDM -OFDM 01001 24 QPSK1/2 SDM -OFDM 01101 36 QPSK 3/4 SDM -OFDM 10001 48 16QAM 1/2 SDM -OFDM10101 72 16QAM 3/4 SDM -OFDM 00001 96 64QAM 2/3 SDM -OFDM 00101 10864QAM 3/4 SDM -OFDM

As shown in Table 1, when the R4 bit is established to be 1, the data isreceived in the IEEE 802.11a method. Because the transmission mode isthe IEEE 802.11a mode when the R4 bit is 1, a value of the antenna bit Ahas no effect, and the configuration of the signal symbol corresponds tothat of the IEEE 802.11a.

However, when the R4 bit is established to be 0, the system is the MIMOsystem. At this time, it is determined whether the transmit mode is theSDM mode or the STBC mode with reference to the antenna bit A.

The R1 to R3 bits respectively correspond to information on eight datarates, mapping methods, and code rates.

Accordingly, the signal symbol is configured by combining 24 bits in alike manner of the conventional signal symbol The 24 bits include lengthof 12 bits, parity of 1 bit and fail of 8 bits. The data is transmittedon the 64 or repeated 128 (64+84) subcarriers in the conventional IEEE802.11a mode, and the data is separately transmitted on the evensubcarriers and the odd subcarriers in the multiple antenna mode asshown in Math FIG. 4 and Math FIG. 8.

In terms of the output of the transmit antenna, predetermined preambleand signal symbol configurations are formed regardless of the number ofthe transmit antennas and bandwidths.

In the above frame configuration, a process for maintaining thecompatibility by the conventional system and the system according to theexemplary embodiment in the receive terminal will be described.

When the data is transmitted in the conventional IEEE 802.11a system,the conventional receiver may perform a demodulation of the shortpreamble, the first long preamble, and the signal symbol field. However,when the signal symbol is interpreted, the data following the signalsymbol is demodulated because the frame corresponds to the conventionalframe when the R4 bit of the RATE bits is 1, the data demodulation isnot performed until the frame ends because the frame is not demodulatedby the conventional demodulator when the R4 bit is 0, Accordingly, thecompatibility is provided in a network formed by combing theconventional system and the system according to the exemplary embodimentof the present invention.

The receiver of the system according to the exemplary embodiment of thepresent invention starts to perform demodulating of the data followingthe signal symbol after the receiver acknowledges that the frame is theIEEE 802.11a frame when R4 of the signal symbols is 1, When the R4 is 0,however, the receiver performs the channel estimation by using thesecond long preamble following the signal symbol, searches the antennabit A, determines whether the transmit mode is the SDM-OFDM or theSTBC-OFDM, and restores the transmit data after a proper demodulationprocess according to the determined mode.

Accordingly the system according to the exemplary embodiment of thepresent invention is allowed to be compatible with the conventional IEEE802.11a system.

FIG. 7 shows a block diagram for representing a configuration for aninitial synchronization of the receiver according to the exemplaryembodiment of the present invention.

In FIG. 7, the receiver includes DC-offset compensators 300 a and 300 b,and inphase and quadrature (I/O) compensators 310 a and 310 b forcompensating I/O mismatch, for a path of the respective antennas. TheDC-offset compensator 300 a and 300 b eliminate a DC-offset on the pathof the respective antennas which may be generated in an analog and RFcircuits. The I/O compensators 310 a and 310 b compensate the I/Omismatch which may be generated in the analog and RF circuits.

The data before the signal symbol, which are the short preamble part andthe first long preamble part, is input to a channel mixer 400. In thechannel mixer 400, the frequency is shifted by +10 MHz and by −10 MHz inorder to respectively divide two bandwidth 40 MHz signals into channel 0of 20 MHZ and channel 1 of 20 MHz. Accordingly, two outputs aregenerated from the respective antenna paths. The signals pass through alow pass filter (LPF) 410 and the signals are decimated by ½ in order toconvert the signals to 20 MHz bandwidth signals. The initialsynchronization is performed by using the short preamble and first longpreamble of 20 MHz.

A carrier frequency offset (CFO) estimator 430 estimates a carderfrequency offset by using an auto-correlation of the short preamble andthe first long preamble. A carrier offset (CFO) compensator 320 a, 320 bcompensates the carrier frequency offset based on the estimated valueoutput from the CFO estimator 430.

A frame synchronizer 420 performs frame synchronization by using a crosscorrelation of the short preamble and the first long preamble. Abandwidth detector 440 performs bandwidth detection for determining theoperational bandwidth by using the auto correlation of the first longpreamble.

The signal symbol including the first long preamble and the data partare input to FFT units 330 a and 330 b after the initial synchronizationis performed. At this time, the channel is estimated and the signalsymbol is demodulated by using an FFT output of the first long preamble.

The signal symbol is demodulated without having information on thetransmit mode because a method for transmitting the signal symbol isalways the same. After the signal symbol is demodulated, the informationon the transmit mode, operational bandwidth, frame length, demodulationmethod, and code rate is provided.

As described above, when the R4 is 1 (that is, when the transmit mode isthe MIMO-OFDM mode), a channel estimator 450 further performs thechannel estimation by using the second long preamble.

The data field is demodulated with reference to the informationestablished in the signal symbol when the channel estimation isperformed.

Phase compensator 340 a and 340 b estimate and compensate residualfrequency and phase offsets by using the pilot subcarrier.

The signal is detected according to the transmit mode by the detector300, and the receiver combines the data passed through the demapper, thedeinterleaver, the Viterbi decoder, and the descrambler and transmitsthe combined data to a media access control (MAC) layer.

Therefore, the system supporting the multiple antennas facilitates thechannel estimation and provides the compatibility with the conventionalsystem.

FIG. 8 shows a flow chart for representing a method for transmitting thedata according to an exemplary embodiment of the present invention.

The binary data generated in the source unit are distributed to theplurality of bandwidths in step S100. The data rate may be increased asthe binary data are distributed to the plurality of bandwidths.

The data distributed to the respective bandwidths are respectivelyencoded in step S110 by exemplary using the convolution code forincreasing error correction of data. The scrambling operation may befurther performed before the encoding operation.

The interleaving operation for preventing a burst transmit error isperformed, and the binary data are mapped into a plurality of complexsymbols in step S120 when the data are encoded. The mapping methodincludes the BPSK, QPSK, 16QAM, and 64QAM modulations.

The data mapped into the complex number symbols are distributed to theantennas, and the subcarriers allocated to the respective antennas areallocated to the distributed complex symbols in step S140. The OFDMsignals formed by allocating the subcarriers respectively perform theinverse fast Fourier transform, to transform the frequency domain signalto the time domain signal.

When the subcarriers are allocated, the signal fills the desiredbandwidths, and 0 fills other bandwidths. The subcarriers may be alsoallocated such that a subcarrier used by an antenna may not be used byanother antenna.

Not only the multiple bandwidths and antennas but also a singlebandwidth and a single antenna may be also used in steps S100 and S130.

When the single bandwidth and antenna are used, the data modulationprocess corresponds to that of the conventional IEEE 802.11a.

Accordingly, it is determined whether the OFDM signal is to betransmitted according to the MIMO transmit method using the multiplebandwidths and antennas in step S150. The information for determiningthe MIMO state is determined by searching the configuration and previousoperation of the transmitter.

When the OFDM signal is to be transmitted according to the MIMO transmitmethod using the multiple antennas, the preambles for the respectivesubcarriers are generated in step S160. The preamble includes the longpreamble of the operational antennas and subcarriers. The long preambleincludes the first long preamble for the channel estimation of theoperational subcarriers of the antenna and the second long preamble forthe channel estimation of the subcarriers which are not used.

At this time, the first long preamble which has been used for asubcarrier by an antenna may be used for the second long preamble.

The signal symbol having information on the data demodulation isgenerated in step S161. The signal symbol is generated by mapping theinformation on the transmit mode, the data rates the mapping method, andthe code rate on the bits R1 to R4 and the antenna bit as shown in Table1.

The data field and the frame for the MIMO antenna are generated by usingthe generated short preamble, the first long preamble, and the secondlong preamble in step S162. The frame is configured in an order of theshort preamble, the first long preamble, the signal symbol, the secondlong preamble, and the data field.

When it is determined that the OFDM signal is not to be transmittedaccording to the MIMO transmit method, the frame for the single antennais generated in step S170 in a like manner of the conventional system.The frame for the single antenna also includes a short preamble, a longpreamble, a signal symbol, and a data field. A description of thegeneration of the frame for the single antenna which has been describedabove will be omitted.

The frame generated by the above configuration is transmitted to thereceiver through the RF transmit unit in step S180.

FIG. 9 shows a flowchart for representing a method for receiving thedata according to an exemplary embodiment of the present invention.

In the method for receiving the data, the OFDM signal received throughthe radio channel is initially synchronized in step S210. In addition,the DC offset is eliminated by using a filter, and the I/Q discordanceis compensated in step S210. The short preamble and the first longpreamble before the signal symbol are used to perform the initialsynchronization of the compensated signal.

The subcarrier frequency offset is estimated by using theauto-correlation of the short preamble and the first long preamble, andthe frame synchronization is performed by using the cross-correlation ofthe short preamble and the first long preamble in step S220.

The bandwidth detection is performed for determining the operationalbandwidth by using the auto correlation of the first long preamble instep S230.

A first channel estimation is performed by the fast Fourier transform ofthe first long preamble in step S240. Methods for the initial timingsynchronization, frequency synchronization, and channel estimation areeasily selected by those skilled in the art because a physical layerconvergence procedure (PLCP) preamble which is a train signal for thesynchronization has been defined in the IEEE 802.11a.

The receiver demodulates the signal symbol and determines theinformation on the signal symbol in step S2S0. The signal symbolincludes information on transmit mode, data rate, mapping method, andcode rate.

The receiver determines whether the demodulated signal symbol istransmitted from the MIMO system with reference to the transmit modeinformation in step S260. The transmit mode information is given basedon an establishment value of the R4 hit among the signal symbols.

When the transmit mode is the MIMO-OFDM mode, the channel estimation isperformed by using the second long preamble transmitted after the signalsymbol. The first long preamble of a subcarrier which is not used byanother antenna is substituted for the second long preamble.Accordingly, the channel estimation on the MIMO-OFDM signal is finishedwhen the second estimation is performed S270.

The phase offset is compensated by using the pilot subcarrier, and thedata demodulation is performed according to the data rate, mappingmethod, and code rate in the signal symbol S280. The data demodulationhas been described with reference to FIG. 3.

When the transmit mode is not the MIMO-OFDM mode in the previous stepS260, the phase compensation and the data demodulation are performedwithout performing another channel estimation.

According to the exemplary embodiment of the present invention, thehigh-speed data rate is provided by the MIMO-OFDM system, and thecompatibility with the conventional system is also provided because mostof the frame configuration of the conventional single antenna OFDMsystem is maintained in the exemplary embodiment of the presentinvention.

While the present invention has bean described in detail with referencesto the preferred embodiments, those skilled in the art will appreciatethat various modifications and substitutions can be made thereto withoutdeparting from the spirit and scope of the present invention as setforth in the appended claims.

1-9. (canceled)
 10. An apparatus in a wireless communication system, theapparatus comprising: a receiver configured to receive a frame, theframe comprising: a short preamble, a first and a second long preamblespositioned subsequent to the short preamble, a first bit streampositioned between the first long preamble and the second long preamble,wherein the first bit stream comprising at least one bit, and a datafield positioned subsequent to the second long preamble; and a circuitryconfigured to determine, based on information in the first bit stream,whether or not the frame is transmitted using space time block coding.11. The apparatus of claim 10, wherein the second long preamblecomprises a third long preamble and a fourth long preamble.
 12. Theapparatus of claim 11, wherein the first long preamble is preceded by aguard interval having a length of 1.6 μsec, each of the third and fourthlong preambles is respectively preceded by a guard interval having alength of 0.8 μsec, and the data field is preceded by a guard intervalhaving a length of 0.8 μsec.
 13. The apparatus of claim 10 or 12, theframe further comprises a second bit stream positioned between the firstlong preamble and the second long preamble, wherein: the second bitstream comprises information whether or not the frame is transmitted ina multiple-input/multiple-output (MIMO) mode, the second bit streamcomprising at least one bit, and the first bit stream and the second bitstream are different.
 14. The apparatus of claim 10 or 12, the framefurther comprises a third bit stream positioned between the first longpreamble and the second long preamble, wherein: the third bit streamcomprises information indicating whether or not the frame is transmittedthrough a single spatial stream, the third bit stream comprising atleast one bit, and the first bit stream and the third bit stream aredifferent.
 15. The apparatus of claim 12, wherein: the short preamblecomprises synchronization information, and the second long preambleprovides reference for the apparatus to form a channel estimate thatallows the apparatus to demodulate the data field.
 16. The apparatus ofclaim 12, wherein the first and second preambles are generated based ona predetermined sequence.
 17. The apparatus of claim 16, wherein: afrequency domain signal of the first long preamble corresponds to afirst sequence being derived from the predetermined sequence, afrequency domain signal of the second long preamble corresponds to asecond sequence being derived from the predetermined sequence, the firstlong preamble is generated by inverse Fourier transform of the firstsequence, and the second long preamble is generated by inverse Fouriertransform of the second sequence.
 18. The apparatus of claim 12,wherein: the first and second long preambles are time domainrepresentations of a first and second long sequence, respectively, andwherein the first and second long sequences are generated based on abasic long sequence, and the basic long sequence comprises, as itselements, A×{1, 1, −1, −1, 1, 1, −1, 1, −1, 1, 1, 1, 1, 1, 1, −1, −1, 1,1, −1, 1, −1, 1, 1, 1, 1, 0, 1, −1, −1, 1, 1, −1, 1, −1, 1, −1, −1, −1,−1, −1, 1, 1, −1, −1, 1, −1, 1, −1, 1, 1, 1, 1}, where A is anon-zeroreal-valued coefficient, and wherein the second long sequence is equalto a sequence obtained by changing values of some, but not all, elementsof the basic long sequence.
 19. A wireless communication methodcomprising: receiving a frame, the frame comprising: a short preamble, afirst and a second long preambles subsequent to the short preamble, afirst bit stream positioned between the first long preamble and thesecond long preamble, wherein the first bit stream comprising at leastone bit, and a data field positioned subsequent to the second longpreamble; and determining, based on information in the first bit stream,whether or not the frame is transmitted using space time block coding.20. The method of claim 19, wherein the second long preamble comprises athird long preamble and a fourth long preamble.
 21. The method of claim20, wherein the first long preamble is preceded by a guard intervalhaving a length of 1.6 μsec, each of the third and fourth long preamblesis respectively preceded by a guard interval having a length of 0.8μsec, and the data field is preceded by a guard interval having a lengthof 0.8 μsec.
 22. The method of claim 19 or 21, the frame furthercomprises a second bit stream positioned between the first long preambleand the second long preamble, wherein: the second bit stream comprisesinformation whether or not the frame is transmitted in amultiple-input/multiple-output (MIMO) mode, the second bit streamcomprising at least one bit, and the first bit stream and the second bitstream are different.
 23. The method of claim 19 or 21, the framefurther comprises a third bit stream positioned between the first longpreamble and the second long preamble, wherein: the third bit streamcomprises information indicating whether or not the frame is transmittedthrough a single spatial stream, the third bit stream comprising atleast one bit, and the first bit stream and the third bit stream aredifferent.
 24. The method of claim 21, wherein: the short preamblecomprises synchronization information, and the second long preambleprovides reference for a receiving apparatus to form a channel estimatethat allows the receiving apparatus to demodulate the data field. 25.The method of claim 21, wherein the first and second preambles aregenerated based on a predetermined sequence.
 26. The method of claim 25,wherein: a frequency domain signal of the first long preamblecorresponds to a first sequence being derived from the predeterminedsequence, a frequency domain signal of the second long preamblecorresponds to a second sequence being derived from the predeterminedsequence, the first long preamble is generated by inverse Fouriertransform of the first sequence, and the second long preamble isgenerated by inverse Fourier transform of the second sequence.
 27. Themethod of claim 26, wherein: the first and second long preambles aretime domain representations of a first and second long sequence,respectively, and wherein the first and second long sequences aregenerated based on a basic long sequence, and the basic long sequencecomprises, as its elements, A×{1, 1, −1, −1, 1, 1, −1, 1, −1, 1, 1, 1,1, 1, 1, −1, −1, 1, 1, −1, 1, −1, 1, 1, 1, 1, 0, 1, −1, −1, 1, 1, −1, 1,−1, 1, −1, −1, −1, −1, −1, 1, 1, −1, −1, 1, −1, 1, −1, 1, 1, 1, 1},where A is anon-zero real-valued coefficient, and wherein the secondlong sequence is equal to a sequence obtained by changing values ofsome, but not all, elements of the basic long sequence.
 28. An apparatusin a wireless communication system, the apparatus comprising: a receiverconfigured to receive a frame, the frame comprising: a first portion, asecond portion subsequent to the first portion, a third portionsubsequent to the second portion, a fourth portion subsequent to thethird portion, and a fifth portion subsequent to the fourth portion,wherein: the first portion comprises a short preamble, the secondportion comprises a first long preamble, the third portion comprisesinformation about space time block coding, the fourth portion comprisesa second long preamble, and the fifth portion comprises a data field;and a circuitry configured to determine, based on information in thethird portion, whether or not the frame is transmitted using space timeblock coding.
 29. The apparatus of claim 28, wherein the second longpreamble comprises a third long preamble and a fourth long preamble. 30.The apparatus of claim 29, wherein the second portion is preceded by aguard interval having a length of 1.6 μsec, each of the third and fourthlong preambles is respectively preceded by a guard interval having alength of 0.8 μsec, and the fifth portion is preceded by a guardinterval having a length of 0.8 μsec.
 31. The apparatus of claim 28 or30, wherein the third portion further comprises information whether ornot the frame is transmitted in a multiple-input/multiple-output (MIMO)mode.
 32. The apparatus of claim 28 or 30, wherein the third portionfurther comprises information indicating whether or not the frame istransmitted through a single spatial stream.
 33. The apparatus of claim30, wherein: the short preamble comprises synchronization information,and the second long preamble provides reference for a receivingapparatus to form a channel estimate that allows the receiving apparatusto demodulate the data field.
 34. The apparatus of claim 30, wherein thefirst and second preambles are generated based on a predeterminedsequence.
 35. The apparatus of claim 34, wherein: a frequency domainsignal of the first long preamble corresponds to a first sequence beingderived from the predetermined sequence, a frequency domain signal ofthe second long preamble corresponds to a second sequence being derivedfrom the predetermined sequence, the first long preamble is generated byinverse Fourier transform of the first sequence, and the second longpreamble is generated by inverse Fourier transform of the secondsequence.
 36. The apparatus of claim 30, wherein: the first and secondlong preambles are time domain representations of a first and secondlong sequence, respectively, and wherein the first and second longsequences are generated based on a basic long sequence, and the basiclong sequence comprises, as its elements, A×{1, 1, −1, −1, 1, 1, −1, 1,−1, 1, 1, 1, 1, 1, 1, −1, −1, 1, 1, −1, 1, −1, 1, 1, 1, 1, 0, 1, −1, −1,1, 1, −1, 1, −1, 1, −1, −1, −1, −1, −1, 1, 1, −1, −1, 1, −1, 1, −1, 1,1, 1, 1}, where A is anon-zero real-valued coefficient, and wherein thesecond long sequence is equal to a sequence obtained by changing valuesof some, but not all, elements of the basic long sequence.
 37. Awireless communication method comprising: receiving a frame, the framecomprising: a first portion, a second portion subsequent to the firstportion, a third portion subsequent to the second portion, a fourthportion subsequent to the third portion, and a fifth portion subsequentto the fourth portion, wherein: the first portion comprises a shortpreamble, the second portion comprises a first long preamble, the thirdportion comprises information about space time block coding, the fourthportion comprises a second long preamble, and the fifth portioncomprises a data field; and determining, based on information in thethird portion, whether or not the frame is transmitted using space timeblock coding.
 38. The method of claim 37, wherein the second longpreamble comprises a third long preamble and a fourth long preamble. 39.The method of claim 38, wherein the second portion is preceded by aguard interval having a length of 1.6 μsec, each of the third and fourthlong preambles is respectively preceded by a guard interval having alength of 0.8 μsec, and the fifth portion is preceded by a guardinterval having a length of 0.8 μsec.
 40. The method of claim 37 or 39,wherein the third portion further comprises information whether or notthe frame is transmitted in a multiple-input/multiple-output (MIMO)mode.
 41. The method of claim 37 or 39, wherein the third portionfurther comprises information indicating whether or not the frame istransmitted through a single spatial stream.
 42. The method of claim 39,wherein: the short preamble comprises synchronization information, andthe second long preamble provides reference for a receiving apparatus toform a channel estimate that allows the receiving apparatus todemodulate the data field.
 43. The method of claim 39, wherein the firstand second preambles are generated based on a predetermined sequence.44. The method of claim 43, wherein: a frequency domain signal of thefirst long preamble corresponds to a first sequence being derived fromthe predetermined sequence, a frequency domain signal of the second longpreamble corresponds to a second sequence being derived from thepredetermined sequence, the first long preamble is generated by inverseFourier transform of the first sequence, and the second long preamble isgenerated by inverse Fourier transform of the second sequence.
 45. Themethod of claim 39, wherein: the first and second long preambles aretime domain representations of a first and second long sequence,respectively, and wherein the first and second long sequences aregenerated based on a basic long sequence, and the basic long sequencecomprises, as its elements, A×{1, 1, −1, −1, 1, 1, −1, 1, −1, 1, 1, 1,1, 1, 1, −1, −1, 1, 1, −1, 1, −1, 1, 1, 1, 1, 0, 1, −1, −1, 1, 1, −1, 1,−1, 1, −1, −1, −1, −1, −1, 1, 1, −1, −1, 1, −1, 1, −1, 1, 1, 1, 1},where A is a non-zero real-valued coefficient, and wherein the secondlong sequence is equal to a sequence obtained by changing values ofsome, but not all, elements of the basic long sequence.
 46. Theapparatus of claim 28 or 30, the third portion comprises a first bitstream and a second bit stream, wherein: the first bit stream comprisesinformation indicating whether or not the frame is transmitted usingspace time block coding, the second bit stream comprises informationwhether or not the frame is transmitted in amultiple-input/multiple-output (MIMO) mode, the first bit streamcomprising at least one bit, the second bit stream comprising at leastone bit, and the first bit stream and the second bit stream aredifferent.
 47. The method of claim 37 or 39, the third portion comprisesa first bit stream and a second bit stream, wherein: the first bitstream comprises information indicating whether or not the frame istransmitted using space time block coding, the second bit streamcomprises information whether or not the frame is transmitted in amultiple-input/multiple-output (MIMO) mode, the first bit streamcomprising at least one bit, the second bit stream comprising at leastone bit, and the first bit stream and the second bit stream aredifferent.